annoying p0440 code

[sleepingiant]

good day all

my wife has a 1999 malibu. over the last couple of months the check engine light has been coming on with the code p0440. i replaced the fuel cap with a oem one . no luck. i then bought a code reader to clear the code and it lasts about 2 days before coming on again. i changed the purge valve and cleared the code... 2 days back on replaced the carbon canister cleared the code 2 days and back on. a garage originally looked at the vehicle and said all the hose look good. the reader indicates no flow detected at the purge valve... i do have a new check valve but i am stumped other than it is a bad hose somewhere...
any ideas would be greatly appreciated

[Triple-X08]

could be a fault in the pcm, or wiring, depends. you need to see if the purge solenoid is working, it may be working fine mechanically, but electrically it may not be getting a signal from the pcm. so you need to check it, change the duty cycle on it, increase it, and feel it, see if it clicks, or you can put a test light in place make sure power and grounds are ok. some are different to others.

basically if the phone isnt ringing then no one can answer it.

have you smoke tested it?

[sleepingiant]

thanks for the come back. the dealer did a smoke test and was ok.
i have checked the wiring as best as i can and it seems fine ,no fuses blown. etc.

this did not happen until after she had the fuel filter changed so i thought the garage knocked off a hose and didn't get it back on or cut one.
since we live in northern ontario and the car is 10 years old could the vent valve be blocked in some way. the new one that i have and has not been installed looks like it has an opening for air to get into. also i followed one line from the purge solenoid back to the pcv valve. with engine running there was lots of vacuum

[MrCritical]

If it's a non-ACDelco filter, it could not be sealing properly, therefore throwing your code.

[73ChevelleSS]

There is more to fixing a P0440 then just doing a smoke test.You need someone who actually knows what they are doing.It sounds like your dealer is a little lacking in knowledge IMO.What about the filler neck,is the vent valve operating correctly?I would return to the dealer and have them recheck the system.

[Ryan066]

have you replaced vent solenoid/valve? thats like the most commen thing that will set that code... use a tech II to activate it .. should hear/feel it click making sure its opening/closing...

[S&W]

I had a 99 malibu with P0440. Cleared code and after the monitors went one by one from 'INC" to "ok" ,(a few days), the code was back on. Last monitor to clear was Evap. Sytem Monitor. As soon as it cleared to "ok" , bingo...it was back on. Trace hoses. Start at PCV (change if stuck open or closed. it should rattle). Then to vacuum regulator (right below the coil packs), next on to a "schrader valve" near the brake vacuum booster. Then down two feet to the steel line that heads to the charcol canister behind the gas tank. (It runs alongside the fuel supply and fuel retun lines.) Pull off the connector at the canister and verify vacuum. Put a touch of silicone grease on this o-ring. Next, disconect the purge solenoid valve assembly from the 1" hose that comes from the charcol canister. Remove the wire connector. Take the assembly apart, (there are 3 or 4 plastic snaps that hold it together). Inspect for damage, debris. Put 12V across the terminals. You should hear it "click" on and off each time you touch it with 12v. Verify that it opens and closes as it clicks. A quick shot of spray lube can help, but replace if its sticking. If nothing else you've inspected most of the plumbing! Hope this helps.